Home nodeB (HNB) mobility in UTRAN R9 may apply in cases when a wireless transmit/receive unit (WTRU) (also referred to herein as user equipment (UE)) is in either an idle or connected mode. In the former mode, the WTRU may move into (or out of) an HNB by performing cell reselection that may need to fulfill several criteria, which may include signal strength and membership status. The WTRU may know whether or not it is a member of a closed subscriber group (CSG) cell or hybrid cell to which a HNB belongs by comparing a CSG identity (CSG ID) that it has in its whitelist with the CSG ID that is broadcast by a CSG cell. It is noted that a cell is known to be a CSG or hybrid cell by checking the value of the CSG indicator bit in the MIB. Moreover, the CSG ID may be retrieved by reading SIB3. Idle mode reselection into a HNB may be executed by the WTRU without interaction with the source base station (e.g., NB or HNB).
In Cell_DCH connected mode, the WTRU may be handed over to an HNB based on possible proximity indications and measurement reporting. In order to send a proximity indication (which may indicate that the WTRU is entering or leaving a location where a CSG cell or hybrid cell may exist), the WTRU may first be configured to do so via radio resource control (RRC) messaging. If the WTRU sends a proximity indication, the NB may send a request to the WTRU to perform measurements on certain cells and may read and report the CSG ID from the cell and whether the WTRU is a member or not.
Although HNB mobility in a cell forward access channel (Cell_FACH) state is typically considered to be a connected mode of operation, with the exception of traffic volume reporting, a WTRU transmitting in Cell_FACH typically does not perform measurement reporting to a base station (e.g., NB or HNB). However, the WTRU may still measure other cells (e.g., inter-frequency or inter-RAT) for example for the purpose of performing cell reselection. The WTRU, if it reselects to another cell, may then perform a cell update procedure for example to let a UTRAN know about its new location at the cell level as the WTRU can receive user plane and control plane data in Cell_FACH. Even if the WTRU does not reselect to a new cell in Cell_FACH, the WTRU can perform a cell update procedure (e.g., upon expiration of a periodic cell update timer). In order to perform measurements in Cell_FACH, the WTRU typically makes use of occasions during which no data will be sent to the WTRU—known as FACH measurement occasions. FACH measurement occasions typically have a fixed length that is a multiple of 10 milliseconds and are repeated according to some parameters that are known to the WTRU.
In order to perform inbound mobility to an HNB while in Cell_FACH, a WTRU may need to read the MIB and SIB3 of a HNB for the purpose of identifying the CSG ID and thereafter verify if it is a member or not (based on comparison with the IDs in the WTRU's whitelist). Two problems that may arise are: (1) the FACH measurement occasions may not be long enough for the WTRU to read the MIB and/or SIB3 of the target cell in the other frequency or RAT; and (2) the FACH measurement occasion may not coincide with the time that the MIB and/or SIB3 of the (potential) target HNB are broadcasted. Even though the WTRU may autonomously choose to prolong its measurement occasions in order to acquire the MIB/SIB3 of the HNB cell, it may lose data while doing so since the HNB in the source cell may be unaware of the WTRU's absence.
Another difficulty associated with Cell_FACH mobility involves the procedure of fetching a WTRU's context by a target HNB (i.e., from the source HNB, both of which are connected to the same HNB gateway (HNB-GW)). This difficulty may arise due to the assignment of the same U-RNTI to two or more WTRUs by different HNBs that are connected to the same HNB GW. The contents of the U-RNTI may include a radio network controller identifier (RNC ID) and the serving RNTI (S-RNTI). The RNC ID is the HNB GW's identity. The S-RNTI is allocated by the HNB. If, e.g., two HNBs coincidentally allocate the same S-RNTI to different WTRUs that are served by the HNBs, then the WTRUs may have the same U-RNTI as the RNC ID is common since both HNBs are connected to the same HNB GW. In such a scenario, if a WTRU performs cell update to a potential target HNB (as part of Cell_FACH mobility), the WTRU may provide its U-RNTI for identification. This may allow the target HNB to contact the source HNB for the purpose of fetching the WTRU's context. It is noted that a WTRU context may be identified by a context ID and may contain information about the WTRU's configuration (e.g. RAB information). The target HNB may initially contact the HNB GW and may then provide the U-RNTI of the WTRU in question. The HNB GW may then try to map a context ID based on the provided U-RNTI. However, if two or more WTRUs have the same U-RNTI, then the HNB GW may get two context IDs, one for each of the WTRUs that is allocated to the same U-RNTI. At this point, the HNB GW/target HNB may not fetch the appropriate context of the WTRU due to the non-uniqueness of the U-RNTI.
Other problems related to Cell_FACH mobility involve the handling of neighbor cell lists (NCLs) being configured with mixed CSG cells and non-CSG cells. For example, one issue relates to CSG-capable WTRU behavior when it detects a CSG cell in the NCL that it is not a member of.
Accordingly, there is a need to provide systems and methods to address the aforementioned difficulties.